Loss of colonic tolerance is a significant clinical problem, as it is thought to result in inflammatory bowel disease. The production of IL-10 by T cells plays an important role in maintaining colonic tolerance. However, it is unclear whether IL-10 is produced by T cells responding to specific antigens potentially derived from bacteria, or is expressed on colonic T cells via non-antigen specific stimuli such as cytokines. The goal of this proposal is to address whether antigen specificity is important in selecting Tr1 and IL-10+ regulatory T (Treg) cells in the colon by sequencing the TRAV14 TCRa repertoire in fixed TCR transgenic mice. If our hypothesis is correct, we will observe that the IL-10+ subsets utilize a unique set of TCRs, which may be useful for the generation of TCR transgenic models of Tr1 or IL-10+ Treg cell development. Using the TCR sequencing data, we will select common Tr1 and IL-10+ Treg TCRs to determine whether they recognize bacteria, and whether they facilitate thymic or peripheral T cell development. TCRs which reproducibly result in peripheral Tr1 and IL-10+ Treg cell development can then be used to generate TCR transgenic models to study IL-10 regulation in T cells. Thus, these studies will increase our understanding regarding how the IL-10 producing T cell subset is generated, which may be useful for developing novel therapies for human disease.